The present invention relates to a liquid crystal device employing a ferroelectric liquid crystal and a thin film transistor as a switching device.
A liquid crystal device employing a ferroelectric liquid crystal exhibiting a chiral smectic-C phase is being applied to a memory type display, a high-speed shutter, etc. owing to the fact that the ferroelectric liquid crystal has a bistable state, a display memory property and a high-speed response property. Particularly, the liquid crystal device is considered to be suitable for a large-capacity display having a matrix pixel structure and requiring a large-area display.
In the above-mentioned liquid crystal device of a ferroelectric liquid crystal type, an orientation defect due to the discrepancy in surfaces of layers is easily generated as compared with a TN type liquid crystal device which is usually employed. Once such an orientation defect is generated, it is hard to restore an orientation to an original state. While the orientation defect is caused by the presence of a foriegn matter on the surface of an oriented film and the nonuniformity in an orientation process, it is primarily caused by the deformation of a liquid crystal cell in receipt of an external force, which causes a change in cell gap to generate flow of a liquid crystal in the cell. This defect causes an adverse affect on display characteristics such as a reduction in display contrast and a change in threshold voltage.
Further, the liquid crystal device of the ferroelectric liquid crystal type conducts displaying by utilizing a double refraction effect of a liquid crystal molecule. Accordingly, it is necessary to make uniform a gap between substrates (which will be hereinafter referred to as a cell gap), and it is further necessary to set the cell gap to a small value of about 2 .mu.m. As a method of forming a small cell gap of about 2 .mu.m, the following method may be considered for example. That is, inorganic particles such as aluminum oxide and silicon dioxide each having a diameter of about 2 .mu.m are dispersed as a spacer between both the substrate, and granular adhesives such as epoxy resin each having a particle size of about 5-10 .mu.m are dispersed. Then, both the substrates are heated to melt the granular adhesives and thereby bond the substrates to each other. In this case, the inorganic particles serve as a spacer to suppress a partial change in the cell gap and thereby make the cell gap uniform.
However, in the liquid crystal device obtained by this method, if the granular adhesives are irregularly dispersed, a plurality of the adhesives are gathered to be united in bonding both the substrates, and in some cases, the adhesives are crushed to become several tens .mu.m in size after bonding both the substrates. As a result, a uniform cell gap cannot be obtained, causing a reduction in display quality. Further, in the event that the granular adhesives are hardened in an aperture, there is no problem in display to be visually observed, but there is a possibility that a display contrast is reduced in a shutter array or the like having a small aperture for a printer. Moreover, in the event that the inorganic particles employed as a spacer are sandwiched between the substrate and a thin film transistor, there is a possibility that the inorganic particles are forced into the thin film transistor to break the same.